The long-term objective of this research is to develop the use of light for the destabilization and/or fusion of lipid bilayer membranes. Photoinduced destabilization of membranes has the potential to provide a selective method of delivery and release of encapsulated reagents to specific sites that are accessible to light via filter optic probes, lasers, or other sources. Photoinduced fusion of membranes offers a new method of initiating and controlling fusion in a spatially and temporally selective manner. We previously demonstrated the light initiated destabilization of bilayer membranes composed of a phosphatidylethanolamine (PE) and a photopolymerizable phosphatidylcholine (PC). Destabilization and fusion occurs as a consequence of the photopolymerization of the PC. The formation of poly-PC appears to proceed with phase separation and enrichment of the nonpolymerized domains in PE, which allows the PE to assume a nonlamellar structure at the ambient temperature. 31p-NMR data indicates that the photoinduced perturbation of the membranes promotes the formation of an isotropic state. The specific research to extend and clarify these observations follows: 1. Determine the necessary and sufficient factors of lipid structure and liposome composition for the efficient photodestabilization and/or fusion of liposomes. 2. Characterize the molecular basis of the membrane perturbation process by 31p-NMR spectroscopy, electron microscopy, calorimeter, and diffraction. 3. Design, synthesize, and evaluate photoinitiators to extend the light sensitivity to visible light of various wavelengths. 4. In collaboration with biological colleagues, evaluate the photoinduced release of therapeutic agents in vitro and in vivo. Finally, this new method of selectively stimulating membrane fusion will both borrow from and contribute to the developing understanding of the polymorphic behavior of lipids and their possible role in biological phenomena.